In petroleum refining, the crude oil systems employed as feedstocks are prone to produce material that deposits and accumulates upon the surfaces of heat transfer equipment contacted therewith resulting in the fouling of petroleum process equipment. In normal, continuous use, for example, the heat exchangers used in almost all crude oil unit processes suffer gradually increasing losses in efficiency, heat transfer, pressure drop, and throughput owing to deposition of material on the inner surfaces thereof. Consequently, crude oil process units must be periodically shut down and the deposits removed or the units replaced. Such fouling of heat exchanger, and also such equipment as furnaces, pipes, reboilers, condensers, compressors, auxiliary equipment, and the like, is costly by reason of the loss of production time and the man hours required for disassembly, cleaning and reassembly of unit process equipment components. The equipment is usually fabricated of carbon steel, stainless steel or aluminum.
The fouling is generally attributed to the presence of unstable components, such as oxidized derivatives of hydrocarbons, the inorganic impurities present in hydrocarbon fractions, the presence of olefinic unsaturated hydrocarbons or their polymeric derivatives, or the like. Thus, almost all crude oil and fractions thereof, as well as process cuts prepared from such, contain minor amounts of readily oxidized and oxidizable hydrocarbon constituents. Furthermore, almost all crude oil contains small amounts of dissolved oxygen, sulfur and metals, in a free and/or chemically combined state. If chemical and/or thermal treatment is involved, the olefinic substitutes may be polymerized.
The use of certain inorganic phosphorus-containing acid materials as antifoulant suppressant additives to mineral hydrocarbon mixtures employed as refinery feedstocks has heretofore been proposed. Thus, Wolff et al U.S. Pat. No. 3,647,677 teaches the addition of such anhydride materials as P.sub.2 O.sub.5 or P.sub.2 S.sub.5 to crude oil for temperatures above 700.degree. F. Koszman et al U.S. Pat. No. 3,531,394 teaches addition of phosphorus materials to petroleum and steam for temperatures ranging from 1000.degree. to 1700.degree. F. in steam cracking. Such additive materials Koszman et al state are in the vapor phase. Gillespie et al in U.S. Pat. Nos. 3,558,470 and 3,645,886 teach the addition of mixtures of (I) phosphorus acid and (II) either a condensation product of carboxylic acid component with alkylene polyamine or a fatty acid ester of alkanol amine. Gillespie et al never use only phosphorus acid as an additive.
So far as we know, no one has heretofore ever employed inorganic phosphorus acid materials, particularly salts thereof such as amine salts as antifoulant reducing additives in crude oil materials in conventional processes thereof. Such phosphorus acids, and salts thereof, have now been found characteristically to display surprising and very useful antifouling reducing activity in crude oil materials. Thus, not only do these materials generally inhibit and suppress and even prevent, fouling when in crude oil materials, but also they unexpectedly appear to reduce the fouling in previously used and fouled crude oil refinery processing equipment. Such additives in combination with one another can sometimes be considered to be arguably synergistic in some of these effects, and applications, as those skilled in the art will appreciate. The art of reducing existing fouling in refining streams is very complex and the reasons why a particular antifoulant system works to reduce fouling effectively in some mineral hydrocarbon mixtures, but perhaps not in others, are not now known.